1. Field of the Invention
The present invention relates to a semiconductor optical device.
2. Related Background of the Invention
There are a variety of structures of semiconductor optical devices, such as a semiconductor laser. For example, publication 1 (IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL.QE-17, NO. 2, FEBRUARY 1981, pp. 202-207) discloses a buried hetero-structure semiconductor laser. This semiconductor laser has an active layer made of GaInAsP semiconductor. This active layer is provided between a p-type InP semiconductor layer and an n-type InP semiconductor layer and is located between InP current block portions of the InP semiconductor layer. Carriers are injected into the active layer and the injected carriers are confined into the active layer by the hetero-barriers at the interfaces between the active layer and the current block portions.